1. Field of the Invention
The present invention relates to a semiconductor integrated circuit having a function switching part for switching a built-in option function.
2. Description of the Related Art
Generally, a semiconductor integrated circuit such as a microcontroller has a common function, which is common to all users, and an option function of which the operating specification can be changed in accordance with the user's wish. Conventionally, in order to switch the option function, the semiconductor integrated circuit has a nonvolatile memory cell, a control circuit that accesses the nonvolatile memory cell, and a latch circuit that latches data read from the nonvolatile memory cell and the like. The control circuit executes a read operation of the nonvolatile memory cell after power-on operation is completed. By latching the read data to the latch circuit, the option function is switched (for example, see Japanese Unexamined Patent Application Publication No. Hei 4-95184, Japanese Unexamined Patent Application Publication No. Hei 6-187468).
In a conventional method, in order to switch the option function, the control circuit needs to perform the read operation by setting the control gate, source and drain of the nonvolatile memory cell to a predetermined voltage. Specifically, the option function can be switched only after a power supply voltage is increased up to a voltage, which is required for operating the control circuit. For example, in the case that the option function is set whenever the power is turned on, the option function can be set only after the power-on operation is completed and thus the power supply voltage is stable. Accordingly, there is a problem in that the period from when the power is turned on to when a normal operation begins becomes long. In a program executable semiconductor integrated circuit such as a microcomputer, the option function must be set in an initializing routine (user program) after the power is turned on. Accordingly, it imposes a heavy burden on a user. Also, there is also a problem in that the size of the control circuit becomes increased.